Method and apparatus for controlling the temperature of a gas distribution plate in a process reactor

ABSTRACT

A plasma process reactor is disclosed that allows for greater control in varying the functional temperature range for enhancing semiconductor processing and reactor cleaning. The temperature is controlled by splitting the process gas flow from a single gas manifold that injects the process gas behind the gas distribution plate into two streams where the first stream goes behind the gas distribution plate and the second stream is injected directly into the chamber. By decreasing the fraction of flow that is injected behind the gas distribution plate, the temperature of the gas distribution plate can be increased. The increasing of the temperature of the gas distribution plate results in higher O 2  plasma removal rates of deposited material from the gas distribution plate. Additionally, the higher plasma temperature aids other processes that only operate at elevated temperatures not possible in a fixed temperature reactor.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.09/944,503, filed Aug. 30, 2001, pending, which is a continuation ofapplication Ser. No. 09/514,820, filed Feb. 28, 2000, now U.S. Pat. No.6,323,133 B1, issued Nov. 27, 2001, which is a divisional of applicationSer. No. 09/026,246, filed Feb. 19, 1998, now U.S. Pat. No. 6,132,552,issued Oct. 17, 2000.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to process reactors usedin fabricating semiconductor devices and, more particularly, to thecontrol of the plasma temperature within the process reactor forimproved reactor fabrication and maintenance operations. Plasma processreactors are used for both etching and depositing material on thesurface of the semiconductor substrate. In either case, a gas isinjected into the chamber of the process reactor where it is ionizedinto a plasma for either etching or reacting with the surface of thesemiconductor substrate to form a desired pattern thereon. It isimportant to control the gas distribution into the reactor as well as tocontrol the temperature of the gas in forming the plasma. Processreactors often use a thermally isolated dielectric plate to control thegas distribution into the reactor. The gases are injected into thechamber on the backside of the dielectric plate and pass through gasinlet holes in the plate to get into the reaction zone.

[0003] The plate is thermally isolated because a backside gap isrequired to allow the process gases to flow behind the plate to the gasinlet holes. This makes the plate temperature and gas temperaturedifficult to control as the process puts a heat load on the plate.

[0004] Attempts have been made to control the temperature by controllingthe temperature of the dielectric plate. Methods of adjusting orcontrolling the temperature have been performed by adjusting thebackside gap to be as small as possible, by controlling the temperatureof the reactor wall located behind it, or by cooling the dielectricplate, or any combination of the three. The heat transfer between theplate and the temperature control reactor wall occurs by conduction ofthe process gas as it flows through the narrow gap. The gas pressure,and not its flow rate, controls how much heat is transferred between thetwo surfaces. The plate temperature is controlled by the gas pressure,the reactor wall temperature, and the heat load on the plate from theprocess chamber.

[0005] A sample plasma process reactor 10 is depicted in the schematicdiagram of FIG. 1. Plasma process reactor 10 includes a plasma chamber12 in which is positioned a substrate holder 14. A semiconductorsubstrate 16 is placed on substrate holder 14. A bias voltage controller18 is coupled to substrate holder 14 in order to bias the voltage tocounter the charges building up on substrate 16. An etching gas isprovided through gas inlet 20, which is ionized by inductor backside 22.Placed upon inductor backside 22 is a plurality of inductor elements 24that is controlled by a current 26. Current 26 causes an inductioncurrent to flow that generates an ionizing field on the interior surfaceof backside 22. The plasma then passes through a gas distribution plate28, which is held in place with a vacuum seal via O-ring 30, allowing agas to pass through a plurality of apertures 32. A second O-ring 34 isplaced between the backside 22 and gas distribution plate 28. A vacuumis created by a vacuum pump 36 for evacuating material and pressure fromchamber 12. A control gate 38 is provided to allow a more precisecontrol of the vacuum as well as the evacuated material. An outlet 40removes the material from the vacuum for disposal.

[0006] In this example, gas distribution plate 28 is made of a siliconnitride material. In certain desired oxide etch processes, it isrequired that the gas distribution plate 28 be cooled below 80° C. Thiscooling is accomplished by cooling the reactor wall of chamber 12 and issometimes called a window in this plasma etch reactor. The reactor wallis cooled to about 20° C. and the process gas is run through thebackside gap. Unfortunately, the temperature of the gas distributionplate 28 cannot be easily modified in this arrangement. The inability tocontrol the temperature causes other problems during different stages ofuse of the process reactor.

[0007] One problem is that cleaning of the interior cannot be easilyperformed since the temperature is fixed as the gas distribution plateis thermally coupled to the reactor wall during cleaning. It is helpfulto run the cleaning process at much higher temperatures than during theetching process, but such an effective cleaning temperature cannot beachieved since the temperature is controlled by the constant gas flow atthe gas distribution plate. Another problem is that processmodifications cannot be performed since only a set maximum temperatureis possible and no higher temperature is available that would allowdifferent processes to be performed that require hotter temperaturesthan those otherwise possible in a fixed-temperature reactor.

[0008] Accordingly, what is needed is a method and apparatus thatovercome the prior problem of being unable to vary the temperature rangeof the process reactor for providing greater control over the processoccurring in the processor reactor. The inability to vary thetemperature range also hinders the cleaning ability of the reactor.

SUMMARY OF THE INVENTION

[0009] According to the present invention, a plasma process reactor isdisclosed that allows for greater control in varying the functionaltemperature range for enhancing semiconductor processing and reactorcleaning. The temperature is controlled by splitting the process gasflow from a single gas manifold that injects the process gas behind thegas distribution plate into two streams where the first stream goesbehind the gas distribution plate and the second stream is injecteddirectly into the chamber. By decreasing the fraction of flow that isinjected behind the gas distribution plate, the temperature of the gasdistribution plate can be increased. The increasing of the chambertemperature results in higher O₂ plasma cleaning rates of the depositson the hotter surfaces. Additionally, where other processes wouldbenefit from warmer gas distribution temperatures, the high gas flowallows higher temperatures to be achieved over the non-split flow of theprior art.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0010]FIG. 1 is a schematic diagram of a plasma process reactoraccording to the prior art;

[0011]FIG. 2 is a schematic diagram of a plasma process reactor having asplit fold plasma manifold and injector according to the presentinvention;

[0012]FIG. 3 is a schematic diagram of a top plan view of a gasdistribution ring providing the secondary gas flow into the chamber;

[0013]FIG. 4 is an alternative embodiment of the gas flow ring used inthe plasma process reactor of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

[0014] A high density, plasma process reactor 100 is depicted in theschematic diagram of FIG. 2. The reactor may have multiple plasmasources where one source is for etching layers in a semiconductorsubstrate while the other source is for depositing a polymer. Reactor100 is a low pressure reactor that operates at or below 50 milliTorr.Low pressure reactors are desired as they avoid microscopic loading,where features of the same size etch more slowly in dense patterns thanin sparse patterns. The reactor 100 has separate controls for top andbottom power. The top power is for energizing high density plasmasources and the bottom power or bias source is for directing the plasmafor etching and for directing a polymer for depositing. The high densityplasma reactor 100 is modeled after an LAM 9100 TCP (transferred coupledplasma) etcher and an Applied Materials HDP 5300. High density plasma isdefined as plasma having an ion density greater than 1×10¹⁰ percentimeter³ in a plasma generation zone. Typically, high density plasmasrange in ion density from 10¹¹ to 10¹³ per cm³.

[0015] Process reactor 100 increases the range of process resultscapable of being obtained as well as improves the ability to clean thechamber by adding a second process gas flow inlet that avoids gaspassing through the gas distribution plate on the backside of thereactor. Reactor 100 is similar in construction to that of the prior artreactor 10 in FIG. 1. Reactor 100 includes a chamber 112 in which isplaced a substrate support platform 114 that holds semiconductorsubstrate material 116. A plurality of substrates 116 can be placed uponsupport platform 114. The bottom bias source is controlled by voltagesupply 118 that either grounds platform 114 or holds it at a selectedvoltage to attract the plasma generated within reactor 100. A firstprocess gas inlet 120 is provided that feeds process gas within achamber formed by reactor backside 122 and gas distribution plate (ordielectric) 128. Gas distribution plate 128 further includes adielectric layer 129, placed on the backside 122 of plate 128.

[0016] A plurality of inductive power sources 124, which is controlledby power supply 126, is mounted to the backside 122 for inductivelycoupling energy to form the plasma that is emitted through apertures 132in gas distribution plate 128. A first O-ring 130 is used to seal gasdistribution plate 128 in place within chamber 112 and a second O-ring134 is used to form the chamber between backside 122 and gasdistribution plate 128. Process reactor 100 further includes a secondprocess gas inlet 142 as well as an auxiliary oxygen inlet 144; bothinlets provide gas flow into chamber 112 and thus bypass gasdistribution plate 128. By splitting the process gas flow into chamber112 via first inlet 120 and second inlet 142, the fractional flowdecreases that flows behind the gas distribution plate 128, thusallowing the temperature of plate 128 to increase. Inlets 120, 142, and144 can be controlled by a mechanical valve (not shown) that iselectronically controlled to open and close at different times.

[0017] The second inlet 142 actually feeds into a distribution ring 146.In the embodiment of FIG. 2, a pair of distribution rings 146, 148 areplaced within the reactor, one above substrate 116 and anothersubstantially coplanar to substrate 116. In using distribution ring 146,it is an annular ring with gas vents that point downwardly towardssubstrate 116. The ring 146 is annular and thus provides a radial gasflow symmetrical to the substrate 116. The alternative ring 148, whichmay be used in tandem with the first ring, has jets 150 that direct thegas flow upward and radially inward for uniform distribution tosubstrate 116.

[0018] The use of the additional inlet valves allows reactor 100 toimprove its cleaning ability as well as provide process modifications.When the process gas is 100% injected through the side, the cooling ofthe dielectric layer 129 on plate 128 diminishes and the O₂ plasma cannow clean deposits from the gas distribution plate 128 because it isthermally uncoupled from the reactor backside 122 during the cleaningstep. Further, residue, such as fluorocarbon polymers, is quickly andmore efficiently cleaned off of gas distribution plate 128 because ofthe higher temperature.

[0019] Process modifications are possible now in that if conditionsrequire high gas flows to occur but also require a warmer gasdistribution plate, the split flow allows the plate to operate at highertemperatures than the prior method of just passing process gas throughgas distribution plate 128.

[0020] Importantly, the change in gas temperature isinversely-proportional to the change in pressure within chamber 112.Accordingly, by reducing the pressure behind gas distribution plate 128,the temperature of the gas flow can increase by bypassing gasdistribution plate 128.

[0021]FIG. 3 is a bottom plan view of a second inlet gas distributionring 146. Ring 146 includes an annular gas vent 152 that has a pluralityof holes 154 distributed around the inner perimeter. The holes can bedirected to point either perpendicular to the plane of distribution ring146 or to point slightly inwardly radially towards the axis of theannular gas vent 152. An inlet connector 156 is provided to attachdistribution ring 146 to the interior of chamber 112. FIG. 4 depicts analternative embodiment of the ring 146. In this embodiment, distributionring 146 has a square or polygonal shaped gas vent 158. A plurality ofholes 154 is provided along the bottom surface of gas vent 158. Again, aconnector 156 is provided to connect distribution ring 146 to the secondinlet 142 within chamber 112. Either ring of FIG. 3 or FIG. 4 can beplaced in the position of ring 146 in FIG. 2. Additionally, either ringcan be placed in a position of distribution ring 148 having jets 150that are substantially coplanar with the substrate 116.

[0022] Referring back to the cleaning operation used to clean processreactor 100, the oxygen is introduced at a partial pressure shown inTable I below: TABLE I PRESSURE AT GAS CHAMBER FLOWS DISTRIBUTION PLATE128 PRESSURE GASES (sccm) (Torr) (mTorr) C₂HF₅ 15 30-40 5-50 N₂ 5 CHF₃15 CH₂F₂ 15

[0023] The approximate temperature behind the gas distribution plate 128is T₁₂₈=80° C. For another example, if the gas flow is split equally(50/50) between the gas distribution plate 128 and the secondary inlet142, the pressure behind plate 128 is between 15-20 Torr, with atemperature approximately T₁₂₈=110° C. As the flow increases at thesecond process gas inlet valve 142, the temperature can increase from50° to 250° C. Table II provides the values for when the flow is either100% through inlet 120 or inlet 142: TABLE II PRESSURE 100% throughInlet 120 100% through Inlet 142 Behind Plate 128 30-500 mTorr 5-500mTorr In Chamber  5-500 mTorr 5-500 mTorr

[0024] The chamber pressure is independent of the pressure behind gasdistribution plate 128. The pressure for 100% of the flow through inlet120 is dependent on O₂ flow rates shown in Table I.

[0025] The present invention may be employed to fabricate a variety ofdevices such as, for example, memory devices. These other devices arenot necessarily limited to memory devices but can include applicationsspecific integrated circuits, microprocessors, microcontrollers, digitalsignal processors, and the like. Moreover, such devices may be employedin a variety of systems, such systems including, but not limited to,memory modules, network cards, telephones, scanners, facsimile machines,routers, copying machines, displays, printers, calculators, andcomputers, among others.

[0026] Although the present invention has been described with referenceto a particular embodiment, the invention is not limited to thedescribed embodiment. The invention is limited only by the appendedclaims, which include within their scope all equivalent devices ormethods which operate according to the principles of the invention asdescribed.

What is claimed is:
 1. A temperature control method for a plasma withina plasma process reactor having a single process gas flow streamthereinto, comprising: splitting said single process gas flow streaminto first gas flow stream and second gas flow stream; introducing thefirst gas flow stream into a first region of the plasma process reactor;and introducing the second gas flow stream into a second region of theplasma process reactor, said introducing the second gas flow stream intothe second region substantially bypassing the first region.
 2. Themethod of claim 1, wherein the first and second gas flow streams areeach introduced as a fraction of the process gas flow from the singlegas stream, the method further comprising: varying a temperature withinat least one of the first and second regions by varying a fraction ofthe process gas flow which flows into the first region.
 3. The method ofclaim 2, further comprising: forming a partial pressure in the firstregion such that the temperature of the plasma increases as the partialpressure decreases.
 4. The method of claim 1, further comprisingevacuating the plasma process reactor.
 5. The method of claim 1, furthercomprising: increasing the temperature of surfaces cooled by gases inthe first region by introducing the second gas flow stream into thesecond region substantially bypassing the first region.